Harry Potter and the Half-Blood Prince represents the immensely popular series' first outing without the net of having new books waiting in the wings. As far as the written word is concerned, Harry's tale is done. Cinematically, there are still two volumes to come (Harry Potter and the Deathly Hallows Parts 1 and 2). The critical question for the movies' producers is whether Harry will be as popular now that his legions of stalwarts know how it all ends. The smart money would be on answering that question with a resounding "yes!" Nevertheless, in part because the source material for the sixth movie is inherently difficult to adapt and in part because of some questionable choices made by screenwriter Steve Kloves in terms of what should be left in and what should be cut out, Harry Potter and the Half-Blood Prince represents the weakest chapter in the franchise since installment #2, Harry Potter and the Chamber of Secrets. After three consecutive top-flight fantasy adventures, Harry has slipped a notch.

One can predict that both fans and non-fans of the books will have issues with the movie, although they likely will not be the same ones. The purists who believe that the novels should be slavish adaptations of J.K. Rowling's tomes may be horrified to learn that a major aspect of The Half-Blood Prince, the development of Voldemort into a more three-dimensional character via an exploration of his history, is largely absent from the film. Those who haven't read the book may be baffled by some things that occur with only cursory explanations, and there are pacing issues. Considering how minimal the core plot is, 153 minutes is too long. A significant number of scenes have apparently been included not because they are critical to events but because Kloves felt there would be a fan uprising if they were eliminated.

As the story begins, Harry (Daniel Radcliffe) and best friends, Ron (Rupert Grint) and Hermione (Emma Watson), are about to begin their sixth year at the Hogwarts School of Witchcraft and Wizardry. With Harry's arch nemesis, Voldemort, tightening the noose around "The Chosen One," Harry finds his enemies are becoming more numerous and deadly. Dumbledore (Michael Gambon), the school's headmaster, shows Harry a selection of key memories about Voldemort's past, but there's a problem - one of the memories, that of Professor Horace Slughorn (Jim Broadbent) discussing forbidden magic, has been distorted. Dumbledore entrusts Harry with the task of befriending the professor and learning the truth of the memory, because it may contain a key to how Voldemort can be defeated. Meanwhile, Draco Malfoy (Tom Felton) seeks revenge against Harry and Dumbledore for the defeat of his father; Professor Snape (Alan Rickman) binds himself by an unbreakable vow to Voldemort's cronies; Harry fights against a growing attraction for Ron's younger sister, Ginny (Bonnie Wright); and Ron and Hermione dance around their feelings for one another.

The Half-Blood Prince suffers from what I call "setup syndrome," meaning that much of its plot and energy is devoted not to telling a self-contained story but to establishing threads that will have a payoff in a future installment. As a result, there's little doubt that The Half-Blood Prince will fare better when the entire series is available. At this point, however, it has an incomplete, unfocused feel. It is easily the least structured of the movies. Fortunately, it ends with a bang, both in terms of visual and emotional impact. The final half-hour is good enough to make one forgive the somewhat meandering nature of the two hours that precede it. For anyone unfamiliar with the novels, some of what happens during the climax may come as a surprise. The Rowling faithful, however, will be interested to see whether the movie does the written word justice with these particular scenes, and I can assure them that it does.

The darkness that has been ever more deeply infusing the Harry Potter movies since The Prisoner of Azkaban is more palpable here than in The Order of the Phoenix. Don't worry about the PG-rating - that just means there aren't any exceptionally gruesome or violent scenes. The Half-Blood Prince continues taking Harry and his friends down a path that leads deeper into the gloaming. Director David Yates' style reflects this. Color is significantly desaturated throughout, and there are scenes (especially those in the cave near the end) that appear almost black-and-white. When one compares the bright, cheery look of Harry Potter and the Sorcerer's Stone with the starkness of The Half-Blood Prince, it can be difficult to accept that the movies are part of the same series.

There are some tonal issues that impede the movie's stability. The light comedy associated with the Ron/Hermione/Lavender romantic triangle, although faithful to the book, isn't entirely successful in the movie, due in part to poor integration. In the book, Rowling was able to incorporate it in a way that felt natural to the characters. In the movie, pretty much every scene in which Lavender appears is drenched in artifice. These sequences seem to belong in an entirely different motion picture. The intent is for them to provide comedic relief, but they often strike the wrong note.

The Half-Blood Prince finally gives Michael Gambon something to do as Dumbledore beyond standing around looking sage. If Ian McKellan's Gandalf could be a wizard of action, why not the headmaster of Hogwarts? It's not a great performance but, given the strictures under which Gambon is working, it's probably the best he could provide. More of a standout is Alan Rickman, whose interpretation of Snape this time around is a richer, more rounded one. Rickman brings something of The Deathly Hallows incarnation of his character into this movie; it can be seen in Snape's eyes, the way he carries himself, and some of his gestures. The lead three teenagers extend what they provided in the previous installments, with Daniel Radcliffe being the most polished, Rupert Grint the most comedic, and Emma Watson the most wooden. Bonnie Wright, who has been lurking around the periphery for most of the series, is a welcome addition to the spotlight, if only because it would be lonely for Ron and Hermione to find each other but for Harry to be left alone.

The revelation that The Deathly Hallows has been bifurcated dims the arrival of The Half-Blood Prince; it is no longer the penultimate motion picture in the saga, but just another stepping stone on the way to the far bank. It is also the least self-contained of the Harry Potter movies. With the five previous productions, it was possible to enjoy them as separate but interconnected adventures (although the previous outing, The Order of the Phoenix, demanded some knowledge of the overall mythos). That is not true of The Half-Blood Prince. It needs to be seen in context. Neophytes will become frustrated and lose their way. This will not vex Potter fans but it may annoy those who have never picked up any of Rowling's books and prefer to view the films as throwaway diversions. The sixth Harry Potter movie has its share of flaws but nevertheless represents solid entertainment, and it extends a remarkable streak for a franchise that has gone six deep without one failure. Two more hits - something entirely possible with the same production team returning and a solid story as the foundation - and the Harry Potter cycle could go down as one of the most creatively rewarding long-running series of all time.